This application claims priority of German Application No. 198 60 712.1 filed Dec. 23, 1998, a copy of which is Attachment A hereto, the disclosure of which is incorporated fully herein by reference.
The invention relates to a film guide for a movie camera.
Film guides for movie films in movie cameras have a distance window positioned in the optical path of rays of the shooting lens of the movie camera, whereby this distance window consists of a picture gate, which determines the size of the area of the individual pictures of the movie film to be exposed, side walls running in the longitudinal direction of the movie film and bordering on the side edges of the movie film, and a platen lying opposite the picture gate, whereby the movie film is moved between these components. Picture gate, platen and side walls thus form a film guiding channel, which fixes the movie film in a picture plane in such a way as to ensure a constant support dimension, i.e. a constant-remaining focusing plane for the movie film during film transport. In the side stems there are grooves or bores for receiving the gripper points as well as possibly a locking gripper of a film transport mechanism for film transport and for ensuring a picture standing position.
Movie films generally consist of an underlay made of triacetate or polyester with high breaking strength and dimensional stability both with normal picture speeds and very high picture speeds, a light-sensitive emulsion applied to one side of the underlay (the front side of the movie film), whereby this emulsion is covered externally by a protecting layer, and a back layer or sliding layer applied to the other side of the underlay, whereby this layer is generally formed in an anti-static way for the purpose of avoiding static flashes on the movie film.
Fundamentally, due to reflections of the shooting rays which arise on the platen, which lies on the back layer of the movie film, undesired changes are brought about in the picture content of the individual pictures of the movie film, which in certain shooting conditions make film-shooting inefficient. This effect occurs in particular with films without an anti-halo layer as well as with black and white films and infra-red films. It is intensified in that in many applications the platen has so-called sliding stems for the purpose of reducing the friction on the movie film, whereby these sliding stems can extend in the movement direction of the movie film or at right angles or diagonally to the movement direction and lie on the back layer of the movie film, in such a way that at these points there is a stronger reflection than on the actual platen, which is reproduced in the picture content as a lattice structure.
It is an object of the present invention to create a film guide with a distance window of the type mentioned above, which ensures exact guiding of the movie film in the picture or focusing plane with minimal friction between the movie film and the film guide and which excludes or minimises changes in the picture content due to ray reflections on the platen.
The solution according to the invention ensures the maintaining of minimal friction of the movie film in the film guide of the distance window, while ensuring exact guiding of the movie film in the region of the picture plane or focusing plane, and while avoiding reflections of the shooting path of rays on the platen as well as distortions of the picture content of the individual pictures of the movie film which are thereby brought about.
If is advantageous if the distance window has platen with black or black-coloured material and sliding stems made from glass carbon (in particular from Sigradur K. glass carbon) which are positioned on it and run parallel to one another in the film transport direction.
For the purpose of easy and cost-effective manufacturing as well as long durability, the sliding stems are preferably stuck on the platen. Through the positioning of the sliding stems in hollows of the platen which run in the longitudinal direction of the film transport, the durability and precise alignment of the sliding stems is further increased. A secure connection between the sliding stems and the platen is thereby ensured even with materials with different heat expansion coefficients, and all in all simple and cost-effective manufacture is also ensured.
Through bevelling the sliding stems at their ends, it is ensured that the movie film is not damaged before it enters the region of the distance window or after leaving the distance window. In addition, it is ensured that no reflections can arise on sharp edges.
Preferably the platen can be inserted in a locking way into the distance window, in such a way that platens of differing kinds can be used for differing film types and/or for differing shooting conditions.
It is particularly advantageous if the distance window is formed as a component of a drive module of the movie camera and can be easily tilted and removed from the drive module as well as being connected to it.